1. Field of the Invention
The present invention relates generally to methods for preparing particles (advantageously submicron-sized particles) of pyrithione salts, and, more specifically, to methods of preparing such particles using de-agglomeration procedures subsequent to production of the particles. The present invention also relates to products made with these particles.
2. Description of the Related Art
Polyvalent metal salts of pyrithione (also known as 1-hydroxy-2-pyridinethione; 2-pyridinethiol-1-oxide; 2-pyridinethione; 2-mercaptopyridine-N-oxide; pyridinethione; and pyridinethione-N-oxide) are known to be effective biocidal agents, and are widely used as fungicides and bactericides in paints and personal care products such as anti-dandruff shampoos. The polyvalent metal salts of pyrithione are only sparingly soluble in water and include magnesium pyrithione, barium pyrithione, bismuth pyrithione, strontium pyrithione, copper pyrithione, zinc pyrithione, cadmium pyrithione, and zirconium pyrithione. The most widely used divalent pyrithione salts are zinc pyrithione and copper pyrithione.
Zinc and copper pyrithione are useful as antimicrobial agents and are active against gram-positive and negative bacteria, fungi, and yeasts. Zinc pyrithione is used as an antidandruff component in shampoos, while technical suspensions of zinc pyrithione and/or copper pyrithione are used as preservatives in paints and polymers. Synthesis of polyvalent pyrithione salts are described in U.S. Pat. No. 2,809,971 to Berstein et al. Other patents disclosing similar compounds and processes for making them include U.S. Pat. Nos. 2,786,847; 3,589,999; 3,590,035; 3,773,770.
Known methods for producing insoluble polyvalent salts of pyrithione result in platelet-shaped (or other irregular shaped) particles having an average size greater than 1 micrometer (xcexcm), and more frequently in the range of 3 to 5 xcexcm. These particles are either used directly, or can be converted into smaller particles. Smaller particles of pyrithione salts (i.e., less than 1 micrometer or xe2x80x9csubmicronxe2x80x9d) are often desired because they more easily form suspensions, emulsions, or dispersions, and provide a larger surface area for enhanced biocidal activity. In addition, smaller particles, particularly in the low submicron range (e.g., below about 0.2 xcexcm are believed to be semi-transparent to light, and below 0.1 xcexcm will be transparent to light). This transparency provides the opportunity to manufacture xe2x80x9cclearxe2x80x9d products, such as clear shampoos and soaps, that are popular in the marketplace today, while providing the larger surface area desired for enhanced biocidal efficacy.
Submicron-sized particles of pyrithione salts are usually generated by a separate mechanical manipulation step (e.g., grinding or crushing) of larger particles or crystals that are made by conventional processes. For example, European Patent Application No. 70046 describes a process for the preparation of zinc pyrithione using organic solvents. This process results in production of large crystals of zinc pyrithione. A separate, optional grinding step is used to grind the large crystals and produce zinc pyrithione particles of smaller size. In another example, U.S. Pat. No. 4,670,430 describes a process of making zinc pyrithione particles with a median size of about 0.2 xcexcm or less by mechanical grinding of larger particles of zinc pyrithione to the desired submicron size. Unfortunately, mechanical grinding of large pyrithione particles into a submicron sized pyrithione particles tends to not produce submicron-sized particles having a desired uniform size, shape and narrow particle size distribution. Such desired parameters are important since they are useful in rendering the behavior of the particles in consumer products, such as shampoos and coatings, predictable. In addition, grinding generally results in substantial loss of useful product and is costly in terms of the equipment, time, and energy required to provide the ground particles. Moreover, a desired particle shape for pyrithione particles, such as rods, needles, or other shapes with potentially enhanced biocidal activity, cannot easily be selected and produced by using grinding methodology.
Submicron-sized particles of pyrithione salts made by the methods of the prior art also suffer from severe agglomeration in which many of the submicron-sized particles bond together through noncovalent interactions to form larger particles of greater than 1 micron in size. Due to high mass, these large agglomerated particles tend to settle out of most consumer products over time and result in a hard packed layer of pyrithione salt that is difficult to re-disperse.
What is needed in the art is a method for producing non-agglomerated or de-agglomerated particles, advantageously having a submicron size or larger, of pyrithione salts possessing a uniform size, shape and/or size distribution. Desirably, the particles, incorporated into a solution, suspension or dispersion, are stable against settling out or agglomerate over time during shipping or storage prior to use. In addition, it is desired that the particles do not exhibit the damage that is typically associated with mechanical grinding. The present invention is believed to provide answers to these needs.
In one aspect, the present invention relates to a method for producing a suspension, emulsion, or dispersion of de-agglomerated (advantageously submicron-sized) particles of pyrithione salts, comprising contacting agglomerated pyrithione salt particles with an de-agglomerating agent, optionally in the presence of sonic energy, to produce said suspension, emulsion, or dispersion of de-agglomerated particles of pyrithione salts.
In another aspect, the present invention provides a method for making de-agglomerated submicron-sized particles of pyrithione salts comprising the steps of:
a) filtering large particles of pyrithione salts is having a particle size in a range of from 1 to 50 microns to provide filtered particles,
b) contacting the filtered particles with at least one de-agglomerating agent selected from the group consisting of electrolytes, surfactants, dispersants, and combinations thereof, to provide a suspension or dispersion of de-agglomerated particles, and
c) heating said de-agglomerated particles to an elevated temperature of at least 60 degrees Centigrade in order to cause a reduction in the size of the de-agglomerated particles to a submicron size, thereby producing said de-agglomerated submicron-sized particles of pyrithione salts.
In yet another aspect, the present invention relates to a suspension, emulsion, or dispersion of de-agglomerated pyrithione particles made by the above methods.
In yet another aspect, the present invention relates to a personal care composition comprising at least one component selected from the group consisting of shampoo, soap, skin care medicament, and combinations thereof, and additionally comprising an antimicrobially effective amount of de-agglomerated particles made by any of the above methods.
These and other aspects will become apparent upon reading the following detailed description of the invention.
It now has been surprisingly found, in accordance with the present invention, that a solution is provided to the problem of producing dispersions of nonagglomerated (advantageously submicron-sized) particles of pyrithione salts. The present inventors have solved this problem by treating particles of pyrithione salts made in a conventional manner with a deagglomerating agent that disperses agglomerated pyrithione salt particles and forms a uniform dispersion of submicron-sized particles of pyrithione salts that do not settle out over time. De-agglomerated particles produced in accordance with the method of the present invention also display a narrow size distribution that make them ideal for use in many consumer products, such as shampoos, coatings, and the like.
The present inventors have unexpectedly discovered that agglomerated particles of pyrithione salts result in part from non-covalent molecular interactions, such as ionic attraction between small particles, and that these non-covalent interactions can be neutralized by treating agglomerated particles made by prior art methods with a de-agglomerating agent. For purposes of the present invention, the de-agglomerating agent may be a surfactant, an electrolyte, a dispersant, or a combination of these. The method of the present invention produces a dispersion, suspension or emulsion comprising particles of pyrithione salts and having numerous advantages when incorporated into personal care products, such as antidandruff shampoos, soaps, and the like. For example, a dispersion of submicron-sized pyrithione salt particles possesses enhanced biocidal activity, relative to such particles having a larger size, due to an increased surface area per unit volume. In addition, the submicron-sized particles that are suitably generated according to the method of the present invention do not re-agglomerate and remain homogeneously dispersed in solution. Prevention of re-agglomeration of the particles is particularly important in the production of personal care products because agglomerated particles, or those that are prone to agglomerate, tend to settle out over time and produce a dense layer of particles on the bottom of containers resulting in an unappealing product having limited utility.
The present inventors have also surprisingly discovered that application of heat (at a temperature of at least 60 degrees Centigrade) to needle shaped pyrithione salt particles having particle sizes in the range of 1-50 microns causes the particles to decrease in size to the submicron range. This finding is particularly advantageous since the needles are easily filtered to remove impurities, whereas submicron-sized pyrithione salt particles are difficult to filter. Therefore, filtration of the needles, followed by de-agglomeration of the needles, and heating to produce the desired purified, submicron-sized particles should prove fruitful to the pyrithione salts manufacturing community.
As used herein, the term xe2x80x9csubmicron-sized particlesxe2x80x9d refers to particles having an average diameter of less than one micron. The term xe2x80x9csuspension, emulsion, or dispersionxe2x80x9d is refers to a homogeneous solution of particles that do not settle out or precipitate over time. The term xe2x80x9cagglomerated pyrithione salt particlesxe2x80x9d refers to particles of pyrithione salts that are bound together by non-covalent forces, such as ionic interactions. The term xe2x80x9cdeagglomerated particlesxe2x80x9d refers to particles that are not bonded together by non-covalent forces. The term xe2x80x9cde-agglomerating agentxe2x80x9d refers to any agent that neutralizes or reduces the non-covalent forces in agglomerated particles.
The term xe2x80x9csonic energyxe2x80x9d is broadly defined to encompass sound waves in the audio sound spectrum, infrasound spectrum, and ultrasound spectrum, preferably in the frequency range of from 20 Hz to 900,000 Hz (900 kHz) with power levels in the range from about 20 to about 5000 watts, more preferably 100 to 1000 watts, most preferably 250 to 750 watts, and decibel (dB) levels from about 10 dB to about 180 dB, preferably 50 to 100 dB, most preferably 65 to 85 dB. The term xe2x80x9csonicationxe2x80x9d, as used herein, refers to application of sonic energy.
As used herein, the term xe2x80x9cwater-soluble salts of pyrithionexe2x80x9d or xe2x80x9cwater-soluble pyrithione saltsxe2x80x9d include those salts of pyrithione in which the hydrogen atom of the thiol group is substituted with a monovalent cation. The term xe2x80x9cwater-soluble polyvalent metal saltxe2x80x9d refers to those water-soluble salts in which the cation has a charge of +2 or greater. The terms xe2x80x9cparticles of pyrithione saltsxe2x80x9d or xe2x80x9cpyrithione salt particlesxe2x80x9d as used herein refer to those salts of pyrithione that form precipitates and are essentially insoluble or sparingly soluble in the surrounding medium. The term xe2x80x9cdispersantxe2x80x9d as used herein refers to a compound that promotes uniform and maximum separation of extremely fine solid particles (i.e., colloidal size), and that does not promote foaming.
An aspect of the present invention relates to a method for treating agglomerated pyrithione salt particles made according to known methods with a de-agglomerating agent to produce a suspension, emulsion, or dispersion of particles (advantageously submicron-sized) particles of pyrithione salts.
Pyrithione salt particles may be made by any process known in the art. In one embodiment, pyrithione or a water-soluble salt of pyrithione is reacted with a water-soluble salt of a selected polyvalent metal in the presence of a dispersant to form pyrithione salt particles as a precipitate. Pyrithione in its acid form, or a water-soluble salt of pyrithione may be used in the reaction. Useful water soluble salts of pyrithione preferably include an ammonium ion or an alkali metal ion such as sodium. Accordingly, exemplary water soluble salts of pyrithione include sodium pyrithione, potassium pyrithione, lithium pyrithione, ammonium pyrithione, and combinations of these. The most preferred water-soluble salt of pyrithione useful in the present invention is the sodium salt (i.e., sodium pyrithione). The amount of pyrithione or water-soluble salt of pyrithione can vary over a wide range and establishing a useful amount is within the capabilities of the ordinary skilled practitioner based on the stoichiometry of the reaction and the required amount of particles that must be generated. A preferred amount of pyrithione or water-soluble pyrithione salt is from about 3% to about 52% by weight of the total weight of the reaction mixture.
Exemplary water-soluble polyvalent metal salts useful in accordance with the method of the invention include example zinc salts, tin salts, cadmium salts, copper salts, silver salts, zirconium salts, magnesium salts, aluminum salts, and the like. Combinations of these salts may also be employed. Useful counterions for these metals include nitrates, acetates, sulfates, halides or combinations thereof. Preferred water-soluble polyvalent metal salts include zinc chloride (ZnCl2), copper chloride (CuCl2), zinc acetate (Zn(O2CCH3)2) and zinc sulfate (ZnSO4) . The amount of water-soluble polyvalent metal salt can vary depending on the amount of water-soluble salt of pyrithione. The molar ratio of pyrithione or water-soluble salt of pyrithione to the water-soluble polyvalent metal salt is generally in the range from about 1:2 to about 1:8. Preferably, a slight stoichiometric excess (e.g., 5% of water-soluble polyvalent metal salt by weight over pyrithione or water-soluble salt of pyrithione) is desirable to ensure a complete reaction.
Useful media or carriers for the reaction include aqueous media such as water, or water in combination with one or more organic solvent(s). Useful organic solvents include alcohols, such as methanol, ethanol, amines such as diethanolamine, ether, esters, and the like.
Optional ingredients such as dispersants, surfactants, pearlizing agents (e.g., TiO2-coated mica), and the like, may also be included in the reaction mixture singly or in any combination. Exemplary dispersants include salts of polymerized alkyl naphthalene sulfonic acids, such as xe2x80x9cDARVAN 1xe2x80x9d (sodium naphthalene sulfonic acid formaldehyde, a product of R.T. Vanderbilt Co. Inc.), xe2x80x9cDEMOL Nxe2x80x9d (sodium salt of naphthalene sulfonic acid, a product of Kao Chemicals), xe2x80x9cDAXAD 11xe2x80x9d (sodium salt of polymerized alkyl naphthalene sulfonic acids, a product of W.R. Grace and Co.), xe2x80x9cTAMOL Nxe2x80x9d (sodium salt of condensed naphthalene sulfonic acid, a product of Rohm and Haas Co.), xe2x80x9cHAROL KGxe2x80x9d (potassium salts of polymerized alkyl naphthalene sulfonic acids, a product of Graden Chemical Co.), xe2x80x9cHAROL RG-71xe2x80x9d (sodium salts of polymerized alkyl naphthalene sulfonic acids, a product of Graden Chemical Co.), xe2x80x9cLOMAR LSxe2x80x9d (sodium salt of condensed mononaphthalene sulfonic acid, a product of Henkel Corp.) and the like.
Exemplary surfactants include nonionics, anionics, cationics, and amphoterics (the latter being also commonly referred to as xe2x80x9czwitterionicsxe2x80x9d). Nonionic surfactants include linear alcohol alkoxylates, such as the linear alcohol ethoxylates, ethyoxylated/propoxylated block copolymers, ethyoxylated/propoxylated fatty alcohols, and polyoxyethylene cetyl ethers, and the like. Useful anionic surfactants include alkyl diphenylether disulfonates, alkyl phenyl ethoxylated phosphate esters, carboxylated linear alcohol alkoxylates, linear alkyl benzene sulfonic acid, diisobutyl sulfosuccinate, alkyl sulfonates, and the like. illustrative cationic surfactants include alkyl triammonium halide, non-linear alkyl dimethyl halide, alkyl dimethyl benzyl ammonium halide-containing surfactants, and the like. Illustrative amphoteric surfactants include polyglycol ether derivatives, ethoxylate oxazoline derivatives, lauramidopropyl betaine, lecithin, and the like.
Generally, these ingredients are utilized in the methods of the present invention in a pyrithione salt-dispersing effective amount, preferably an amount of from about 0.1 to about 20% by weight, more preferably from about 0.1 to about 5% by weight, and most preferably from about 0.1 to about 6% by weight, all based on the total weight of the reaction mixture.
The temperature of the reaction may be any temperature which permits precipitation of particles of pyrithione salt. Preferable temperatures for the reaction are in the range of from between about 4 and about 100xc2x0 C., more preferably between about 25 and about 68xc2x0 C., and most preferably between about 30xc2x0 C. and about 35xc2x0 C.
In addition, the reaction may be gently agitated to promote formation of the particles. Generally, gently stirring the reaction at 150 rpm or less, and preferably about 100 rpm, after all the ingredients have been combined is sufficient to promote formation of the particles.
Additional inorganic salts, such as potassium chloride, sodium chloride, magnesium chloride, the corresponding sulfates, citrates, nitrates, and the like, may be added to the reaction medium to control particle length and shape. For example, suitable addition of salts can result in particles of pyrithione salts having a variety of advantageous shapes, including nonspherical or non-platelet form, such as rods, needles, cylinders, cones, ellipsoids, prisms, parallelepipeds, pyramids, and the like. The particles formed by the present invention may also take the form of tetrahedrons, hexahedrons (cube), octahedrons, dodecahedrons, icosahedrons, and the like. The present inventors have observed that certain shapes of pyrithione salt particles offer advantages of increase biocidal activity due to increased surface area.
Preferably, the additional salts are included in the reaction mixture from 0.1% by weight to about 10% by weight, more preferably from about 1% by weight to about 8% by weight, and most preferably from about 3% by weight to about 6% by weight, all based on the total weight of the reaction mixture.
A particularly useful amount of additional sodium chloride added to the reaction mixture to control particle size and shape is 5% by weight based on the total weight of the reaction mixture.
In one order to produce the elongated particles of the invention, pyrithione or a selected water-soluble salt of pyrithione and a selected water-soluble polyvalent metal salt are reacted in the presence of a surfactant or combination of surfactants in any suitable reaction vessel at a temperature below 70xc2x0 C., and preferably between about 10xc2x0 C. and 68xc2x0 C. In a preferred embodiment, sodium pyrithione is reacted with zinc chloride or zinc sulfate in the presence of salt (e.g., sodium chloride) and a selected surfactant or combination of selected surfactants at about 35xc2x0 C. to form zinc pyrithione having rod or needles shapes, along with aqueous sodium chloride or aqueous sodium sulfate as by-products. The particles may also be utilized in a xe2x80x9ccontinuousxe2x80x9d process in which the zinc pyrithione particles are collected, and the mother liquor containing aqueous sodium chloride or sodium sulfate is recycled back to the reaction vessel to provide a source of additional salt. An optional filter (e.g., carbon or charcoal filter) may be employed to remove impurities such as colored organic compounds from the mother liquor. Particles of zinc pyrithione so formed have a xe2x80x9cneedlexe2x80x9d or xe2x80x9crodxe2x80x9d appearance. Generally, the rods or needles of zinc pyrithione salt produced in accordance with the present invention are between about 0.1 and about 1 xcexcm in width and between about 2 and about 50 xcexcm in length. Accordingly, the aspect ratio of the elongated particles is greater than about 1, and more preferably from about 2 to about 500.
The pyrithione salt particles may be isolated from the mother liquor by filtration, centrifugation, sedimentation, or other isolation methods known in the art. Subsequent procedures, such as grinding, may also be performed. Alternatively, the agglomerated particles in the reaction medium may be treated with a deagglomerating agent directly.
During particle formation, either by the above exemplary method or by other methods known in the art, the individual pyrithione salt particles aggregate into larger agglomerates having sizes greater than about 1 micron. To reduce or eliminate this aggregation and to obtain a population of individual particles having sizes of less than 1 micron, the aggregated particles are treated with a deaglommerating agent to produce a dispersion of submicron-sized particles of pyrithione salts.
The deagglomerating agent used in the method of the present invention may be any agent that separates agglomerated particles of pyrithione salt. Examples of such deagglomerating agents include electrolytes, surfactants, sonic energy, and combinations of these. The inventors have unexpectedly found that treatment of agglomerated particles with a deagglomerating agent neutralizes the noncovalent forces that result in agglomeration of the particles, and results in production of a population of pyrithione salt particles having sizes of less than 1 micron.
Electrolytes used as a deagglomerating agent in the method of the present invention include alkali metal or alkaline earth metal salts (e.g., alkali metal or alkaline earth metal salts of chloride, sulfate, carbonate, citrate, benzoate), alkali metal or alkaline earth metal oxides, alkali metal or alkaline earth metal hydroxides, and combinations thereof. Particularly useful electrolytes include sodium chloride, calcium chloride, zince chloride, sodium oxide, calcium oxide, zinc oxide, sodium hydroxide, calcium hydroxide, and zinc hydroxide. Combinations of two, three, four, or more, of these electrolytes may also be used in accordance with the method of the present invention.
Preferably, electrolytes used according to the method of the present invention range from about 0.01 to 10% by weight, more preferably, from about 0.1 to 5% by weight, and most preferably from about 0.5 to 3% by weight, based on the total weight containing the admixture of aggregated particles (on a dry weight basis).
Dispersants useful in the present invention include salts of polymerized or unpolymerized alkyl naphthalene sulfonic acids. Useful salts of polymerized alkyl naphthalene sulfonic acids include xe2x80x9cDARVAN 1xe2x80x9d (sodium naphthalene sulfonic acid formaldehyde, a product of R.T. Vanderbilt Co. Inc.), xe2x80x9cDEMOL Nxe2x80x9d (sodium salt of naphthalene sulfonic acid, a product of Kao Chemicals), xe2x80x9cDAXAD 11xe2x80x9d (sodium salt of polymerized alkyl naphthalene sulfonic acids, a product of W.R. Grace and Co.), xe2x80x9cTAMOL Nxe2x80x9d (sodium salt of condensed naphthalene sulfonic acid, a product of Rohm and Haas Co.), xe2x80x9cHAROL KGxe2x80x9d (potassium salts of polymerized alkyl naphthalene sulfonic acids, a product of Graden Chemical Co.), xe2x80x9cHAROL RG-71xe2x80x9d (sodium salts of polymerized alkyl naphthalene sulfonic acids, a product of Graden Chemical Co.), xe2x80x9cLOMAR LSxe2x80x9d (sodium salt of condensed mononaphthalene sulfonic acid, a product of Henkel Corp.) and the like. Surfactants used as a deagglomerating agent in the method of the present invention anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants (also known as xe2x80x9czwitterionicsxe2x80x9d), and the like.
Useful nonionic surfactants include linear alcohol alkoxylates, such as the linear alcohol ethoxylates, ethyoxylated/propoxylated block copolymers, ethyoxylated/propoxylated fatty alcohols, and polyoxyethylene cetyl ethers, and the like. Useful linear alcohol alkoxylates are commercially available, for example, under the registered trademark POLY-TERGENT SL-42, a product of Olin Corporation. If desired, the alcohol alkoxylate is suitably end-capped with a lower alkyl group, and such a product is commercially available as POLY-TERGENT SLF-18, a propylene oxide-capped linear alcohol alkoxylate that is also a product of Olin Corporation, and these end-capped linear alcohol alkoxylates are notably low foaming during use. Also advantageous for use in accordance with the present invention are surfactants within the group commercially available as POLY-TERGENT SLF-18B series surfactants, which are surfactants characterized by enhanced biodegradability (also products of Olin Corporation), being alkene oxide-capped linear alcohol alkoxylates, containing ethylene oxide moieties in the backbone, and suitably also containing at least one propylene oxide moiety in the backbone, as disclosed, for example, in U.S. Pat. Nos. 4,925,587 and 4,898,621.
Other useful nonionic surfactants include one commercially available as NEODOL 91-6, a registered trademark surfactant product of Shell Chemical. This surfactant is a detergent range mixture of C9-C11 linear primary alcohol ethoxylates having an average of six moles of ethylene oxide per mole of alcohol. Other useful nonionic surfactants include those containing a linear C9-C11, carbon chain and five or six ethylene oxide or propylene oxide groups per molecule.
Useful anionic surfactants include alkyl diphenylether disulfonates, alkyl phenyl ethoxylated phosphate esters, carboxylated linear alcohol alkoxylates, linear alkyl benzene sulfonic acid, diisobutyl sulfosuccinate, and alkyl sulfonates. Useful anionics also include the alkylated diphenyl oxide sulfonates, and their methods of preparation are well-known, as illustrated by the disclosures of U.S. Pat. Nos. 3,264,242; 3,634,272; and 3,945,437, the disclosures of which are all incorporated herein by reference. Commercial methods of preparation of the alkylated diphenyl oxide sulfonates generally do not produce species which are monoalkylated, monosulfonated, dialkylated or disulfonated. The commercially available species typically are predominately (greater than 90 percent) disulfonated and are a mixture of mono- and di-alkylated with the percentage of dialkylation being about 15 to about 25 percent, and the percentage of monoalkylation being about 75 to 85 percent. Most typically, the commercially available species are about 80 percent monoalkylated and 20 percent dialkylated.
Two illustrative commercially available solutions containing alkylated diphenyl oxide sulfonate surfactants are DOWFAX 8390 and DOWFAX 8390A surfactants, trademarked products of The Dow Chemical Company. In each, the alkyl group is predominantly a hexadecyl C16 group. These products are suitably employed in a solution fully or partially neutralized with ammonium hydroxide if desired.
An advantageous anionic surfactant is also provided by reacting the above-described alkylated diphenyl oxide sulfonates with a piperazine compound to produce a molar ratio of sulfonate compound to piperazine compound of between about 10:1 and about 1:10, preferably between about 2:1 and about 1:2. Although any piperazine compound can be used for such reaction, preferred compounds include those selected from the group consisting of 1,2-aminoethyl piperazine, 1,4-piperazinediethane sulfonic acid, anhydrous piperazine, hydrated piperazine, and combinations thereof.
Other useful anionics are polycarboxylated alcohol alkoxylates, preferably those selected from acids or organic or inorganic salts of the following: polycarboxylated linear alcohol alkoxylates, polycarboxylated branched alcohol alkoxylates, polycarboxylated cyclic alcohol alkoxylates, and combinations thereof. These polycarboxylated alcohol alkoxylates typically contain at least two succinic acid radicals per molecule. Preferred polycarboxylated alcohol alkoxylates are those having a backbone containing both poly(propylene oxide) and poly(ethylene oxide) blocks, and such preferred polycarboxylated alcohol alkoxylates are readily commercially available, for example, as POLY-TERGENT CS-1, a trademarked surfactant of Olin Corporation. If desired, at least a portion of the acid groups on the polycarboxylated alcohol alkoxylate are neutralized with a base to provide the corresponding salt. Suitable bases include alkali metal hydroxides, alkaline earth metal hydroxides, and metal-free hydroxides, including potassium hydroxide, ammonium hydroxide, calcium hydroxide, magnesium hydroxide, ammonia, mono-, di- and tri-ethanol amines, and combinations thereof. Sodium hydroxide is preferred, and although potassium hydroxide can be employed, it is not preferred. The organic or inorganic base is preferably employed in at least an equimolar amount relative to the number of moles of polycarboxylated alcohol alkoxylated used. The polycarboxylated alcohol may also contain a polycarboxylic acid, for example, polyacrylic acid, along with the starting alcohol alkoxylate and esters of the alkoxylate of the polycarboxylic acid.
Although individually the cationic and the amphoteric surfactants are acceptable for use in the process of the present invention, they may also be used in combination with at least one surfactant from one of the other classes. Illustrative cationics include alkyl triammonium halide, non-linear alkyl dimethyl halide and alkyl dimethyl benzyl ammonium halide-containing surfactants. Illustrative amphoteric surfactants include polyglycol ether derivatives, ethoxylate oxazoline derivatives, lauramidopropyl betaine, and lecithin.
Suitable blends can be employed in the process of the present invention based on various combinations of the above-described surfactants. Such a blend can be any combination of two or more surfactants, between or within the above-described four broad classes of surfactants. Combinations can include blends of: anionic with anionic, anionic with nonionic, anionic with cationic, anionic with amphoteric, cationic with cationic, cationic with amphoteric, nonionic with nonionic, nonionic with amphoteric, and amphoteric with amphoteric. Likewise, ternary and quaternary blends of surfactants by selecting three or four surfactants, respectively, from within or among the above-described classes.
Suitably, any single or combination of two, three or four surfactants from the following illustrative list are suitably employed: (a) nonionics, including alkoxylated linear alcohols (such as POLY-TERGENT SLF-18 surfactant, a product of Olin Corporation), linear alcohol ethoxylates (such as NEODOL 91-8 surfactant, a product of the Shell Corporation), ethoxylated linear alkyl benzene (such as TRITON X-100 surfactant, a product of Union Carbide Corporation), and EO/PO block copolymers (such. as POLY-TERGENT E-17A surfactant, a product of Olin Corporation); (b) anionics, including alkyl diphenyl ether disulfonates (such as POLY-TERGENT 2A1 surfactant, a product of Olin Corporation), alkyl phenyl ethoxylated phosphate esters (such as Wayfos M-60 surfactant, a product of Olin Corporation), carboxylated linear alcohol alkoxylates (such as POLY-TERGENT CS-1 surfactant, a product of Olin Corporation), linear alkyl benzene sulfonic acid (such as BIOSOFT S-130 surfactant, a product of Stepan Company), alpha-olefin sulfonates (such as BIO TERG AS-40 surfactant, a product of Stepan Company), dialkylsulfosuccinates (such as AROWET SC-75 surfactant, a product of Arol Chemical Products), and alkyl sulfates (such as STEPANOL SLS surfactant, a product of Stepan Company); (c) cationics including alkyl triammonium halides (such as CTAB surfactant, a product of VWR Scientific Inc.), polyoxyethylene cocoamine (such as MAZEEN surfactant, a product of PPG Industries), primary alkyl amines (such as ARMEEN surfactant, a product of Akzo Chemical Co.), dicoco dimethyl ammonium halide (such as JET QUAT surfactant, a product of Jetco Chemical Inc.), di-isodecyl dimethyl ammonium halides (such as AMMONYX K9 surfactant, a product of Stepan Company), and diethyl aminoethyl stearate (such as CERASYNT 303 surfactant, a product of ISP Van Dyke); and, (d) amphoterics, including polyglycol ether derivatives (such as ALBEGAL A surfactant, a product of Ciba-Geigy), ethoxylated oxazolin derivatives (such as ALKATERG T-IV surfactant, a product of Angus Chemicals), lauramide propyl betain (such as LEXAINE C surfactant, a product of Inolex Chemicals), lecithin (such as CANASPERSE surfactant, a product of Can Amoral), disocium cocoamphodiacetate (such as MONATERICS surfactant, a product of Mona Industries), complex fatty amine salt (such as MAFO 13 surfactant, a product of PPG Industries), and cocoamine oxide (such as MACKAMINE CO surfactant, a product of the McIntyre Group Ltd.). Combinations of two, three, four, or more, of these surfactants may also be used in accordance with the method of the present invention.
Preferably, surfactants used according to the method of the present invention range from about 0.01 to 10% by weight, more preferably, from about 0.025 to 5% by weight, and most preferably from about 0.05 to 1% by weight, based on the total weight of the admixture containing aggregated particles (on a dry weight basis).
Sonic energy is optionally employed in the methods of the present invention in order to facilitate or expedite the desired de-agglomeration being effected by the de-agglomerating agent(s), and to enhance the uniformity of the resulting suspension, dispersion or emulsion. If used, the sonic energy is preferably applied to the agglomerated pyrithione salt particles in the presence of the de-agglomerating agent(s) to form a highly uniform suspension of non-agglomerated particles. The sonic energy preferably has a frequency of from about 20 Hz to about 900,000 Hz (900 kHz), more preferably from about 5 kHz to about 105 kHz, and most preferably from about 16 kHz to about 20 kHz. Combinations of frequencies may also be used, depending on the configuration of the particular sonication apparatus. The energy level output that results from the sonic energy applied to the reaction mixture is preferably in the range from about 20 to about 5000 Watts, more preferably from about 100 to about 1000 Watts, and most preferably from about 400 to about 600 Watts. An example of a suitable sonication device that is useful according to is the method of the invention is a Nearfield NAP Model 3606 acoustical processor (available commercially from Advanced Sonic Processing Systems, Woodbury, Conn.), although any sonication device may be employed in the method of the invention.
It will be noted that the sound levels that could be produced using the levels of sonic energy discussed above can exceed 100 decibels (dB) and potentially reach levels as high as 140 dB. In order to avoid hearing impairment, proper safety and sound abatement procedures should be undertaken when decibel levels are greater than about 80 dB.
Preferably, in the batch process, sonic energy is applied to the reaction mixture through a climate probe that is placed in direct contact with the particles after their formation. Other methods of applying sonic energy are also feasible, such as a pipe which carries the sonic energy to the reaction vessel, or a chamber lined with sonic energy transducers. The latter method is particularly useful in the continuous manufacture of particles as described in copending U.S. patent application Ser. No. (Attorney Docket No. 101715-100, filed on Feb. 23, 1999), incorporated herein by reference in its entirety.
The uniform, well-dispersed suspension of non-agglomerated particles made according to the method of the invention is useful in the production of personal care products (e.g., shampoos, soaps, etc.), cleaning products, paints, coatings, foodstuffs, fertilizers, pool chemicals, foodstuffs, and the like. For example, deagglomerated zinc pyrithione particles made according to the method of the invention are a useful component of antimicrobial-containing shampoos, e.g., as an antidandruff additive in providing an antidandruff efficacy characteristic to shampoos. Generally, the antimicrobial-containing personal care composition of the present invention may contain any xe2x80x9cbase mediumxe2x80x9d component found in shampoos, soaps, or skin care medicaments, such as, for example, glycerine, aloe, surfactants such as dodecyl-benzene sulfonate (xe2x80x9cDDBSxe2x80x9d), mineral oil, water, and combinations thereof. Other such components are described in the examples provided hereinbelow.
The following examples are intended to illustrate, but in no way limit the scope of the present invention. All parts and percentages are by weight and all temperatures are in degrees Celsius unless explicitly stated otherwise. In the following Examples xe2x80x9cq.s.xe2x80x9d means quantity sufficient, generally 0.1 to 2% by weight.